Display and Interface Design

22 Display and Interface Design: Subtle Science, Exact Art
However, from the start of our careers thinking about the design of interfaces
for safety critical systems such as nuclear power plants and aircraft, a
question has nagged us:
What if the mental models of the operators are naive or even wrong?
This possibility was explicitly noted by Norman (1986), who once described
mental models as “messy, sloppy, incomplete, and indistinct” (p. 14). It seemed
obvious that just any mental model would not be sufficient for operating a
nuclear power plant or landing an aircraft safely. Certainly, these systems
behave according to physical principles and it seemed obvious that unless
the thinking (mental model) at least implicitly takes these principles into
account, the control and problem solving might be ineffective and perhaps
dangerous. In thinking about how to design interfaces in these contexts, we
have found it important to ask, “What is the ‘right’ mental model?” Or, more
conservatively, “Are some models more effective or satisfactory than others?
Why?” The point is that the mental model must have some correspondence
with the physical process that is being controlled.
2.3.2 An Ecological or Situated Perspective: Meaning = Affordance
In thinking about this problem of the right conceptual model, we have come
to question the conventional notion of meaning and the conventional notions
about the nature of computational processes. We began to look to the situation
and to frame questions of meaning in this context. We found ourselves
asking how the nuclear power plant and the aircraft actually work. For example,
we began to press beyond questions to pilots about how they thought or
what they did to ask, “Why was that strategy or that procedure adequate?”
In searching for answers to these questions, we had to go beyond the pilots;
we had to begin talking with the aeronautical engineers and we had to begin
learning about aerodynamics.
For example, in a landing approach to a typical airport, pilots generally
begin by setting the throttle to about 70% of full cruising power. They then
fly the glide path using their stick (elevators)—not to point the aircraft at
the point of touchdown, but rather to keep a constant target airspeed. Most
pilots know this strategy. They know that it normally works. However, not
all can explain why this strategy works or are aware of the conditions where
this might not be the safest strategy (e.g., landing on short fields or aircraft
carriers).
In the process of exploring questions about why this works, we learned
about the physics of aviation and the relations between total, kinetic, and
potential energy. We learned a new way to think about the flight controls.
We learned that the throttle’s function is to determine the rate of change of
energy. Depending on the throttle’s setting, total energy will be decreasing
(energy-in is less than energy-out due to drag), increasing (energy-in exceeds
© 2011 by Taylor & Francis Group, LLC